Comments

Fix failed boot after RTC wake-up by making sure RTC-interrupts are
disabled at shutdown.
The RTC-registers are not reset at shutdown when there is backup power
available, and hence the RTC-interrupt, which uses the shared system
interrupt, may be enabled during early boot. If an RTC-alarm goes off
before the RTC-driver is initialised (e.g. when waking up from an
RTC-alarm) this results in disabled system interrupts.
Without earlyprintk boot hangs after
Uncompressing Linux... done, booting the kernel.
and earlyprintk reveals that the shared system interrupt gets disabled:
irq 17: nobody cared (try booting with the "irqpoll" option)
[<c000cf8c>] (unwind_backtrace+0x0/0xf0) from [<c00513ec>] (__report_bad_irq+0x20/0xe8)
[<c00513ec>] (__report_bad_irq+0x20/0xe8) from [<c00516fc>] (note_interrupt+0x1e0/0x244)
[<c00516fc>] (note_interrupt+0x1e0/0x244) from [<c004f980>] (handle_irq_event_percpu+0xac/0x1c4)
[<c004f980>] (handle_irq_event_percpu+0xac/0x1c4) from [<c004faec>] (handle_irq_event+0x54/0x84)
[<c004faec>] (handle_irq_event+0x54/0x84) from [<c0052364>] (handle_fasteoi_irq+0x84/0x154)
[<c0052364>] (handle_fasteoi_irq+0x84/0x154) from [<c004f1f8>] (generic_handle_irq+0x20/0x30)
[<c004f1f8>] (generic_handle_irq+0x20/0x30) from [<c0009b8c>] (handle_IRQ+0x30/0x84)
[<c0009b8c>] (handle_IRQ+0x30/0x84) from [<c0008fa0>] (__irq_svc+0x40/0x6c)
[<c0008fa0>] (__irq_svc+0x40/0x6c) from [<c001cd6c>] (__do_softirq+0x5c/0x164)
[<c001cd6c>] (__do_softirq+0x5c/0x164) from [<c001d268>] (irq_exit+0x58/0x60)
[<c001d268>] (irq_exit+0x58/0x60) from [<c0009b90>] (handle_IRQ+0x34/0x84)
[<c0009b90>] (handle_IRQ+0x34/0x84) from [<c0008fa0>] (__irq_svc+0x40/0x6c)
[<c0008fa0>] (__irq_svc+0x40/0x6c) from [<c03e668c>] (start_kernel+0x1d8/0x29c)
[<c03e668c>] (start_kernel+0x1d8/0x29c) from [<70008040>] (0x70008040)
handlers:
[<c0012df0>] at91sam926x_pit_interrupt
Disabling IRQ #17
Note that disabling the RTC-interrupts at shutdown fixes boot after a
clean shutdown, but that an RTC-alarm after a user (or watchdog) reset
could still prevent the system from booting.
Note also that the only way to recover from a failed boot after an
RTC-alarm is to remove any backup power (e.g. backup battery) or to
disable (or acknowledge) the RTC-interrupt manually from the bootloader.
In particular, a user-reset is not sufficient.
Tested on at91sam9g45.
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
---
drivers/rtc/rtc-at91rm9200.c | 9 +++++++++
1 file changed, 9 insertions(+)